A photovoltaic cell converts radiant energy, such as sunlight, into electrical energy. In practice, multiple photovoltaic cells are electrically connected together in series or in parallel and are protected within a photovoltaic module or solar module.
As shown in FIG. 1, a photovoltaic module 10 comprises a light-transmitting substrate 12 or front sheet, a front encapsulant layer 14, an active photovoltaic cell layer 16, a rear encapsulant layer 18 and a back-sheet 20. The light-transmitting substrate is typically glass or a durable light-transmitting polymer film. The transparent front sheet (also know as the incident layer) comprises one or more light-transmitting sheets or film layers. The light-transmitting front sheet may be comprised of glass or plastic sheets, such as, polycarbonate, acrylics, polyacrylate, cyclic polyolefins, such as ethylene norbornene polymers, polystyrene, polyamides, polyesters, silicon polymers and copolymers, fluoropolymers and the like, and combinations thereof. The front and back encapsulant layers 14 and 18 adhere the photovoltaic cell layer 16 to the front and back sheets, they seal and protect the photovoltaic cells from moisture and air, and they protect the photovoltaic cells against physical damage. The encapsulant layers 14 and 18 are typically comprised of a thermoplastic or thermosetting resin such as ethylene-vinyl acetate copolymer (EVA). The photovoltaic cell layer 16 is made up of any type of photovoltaic cell that converts sunlight to electric current such as single crystal silicon solar cells, polycrystalline silicon solar cells, microcrystal silicon solar cells, amorphous silicon-based solar cells, copper indium (gallium) diselenide solar cells, cadmium telluride solar cells, compound semiconductor solar cells, dye sensitized solar cells, and the like. The back-sheet 20 provides structural support for the module 10, it electrically insulates the module, and it helps to protect the module wiring and other components against the elements, including heat, water vapor, oxygen and UV radiation. The module layers need to remain intact and adhered for the service life of the photovoltaic module, which may extend for multiple decades.
Photovoltaic cells typically have electrical contacts on both the front and back sides of the photovoltaic cells. However, contacts on the front sunlight receiving side of the photovoltaic cells can cause up to a 10% shading loss.
In back-contact photovoltaic cells, all of the electrical contacts are moved to the back side of the photovoltaic cell. With both the positive and negative polarity electrical contacts on the back side of the photovoltaic cells, electrical circuitry is needed to provide electrical connections to the positive and negative polarity electrical contacts on the back of the photovoltaic cells. U.S. Patent Application No. 2011/0067751 discloses a back contact photovoltaic module with a back-sheet having patterned electrical circuitry that connects to the back contacts on the photovoltaic cells during lamination of the solar module. The circuitry is formed from a metal foil that is adhesively bonded to a carrier material such as polyester film or Kapton® film. The carrier material may be adhesively bonded to a protective layer such as a Tedlar® fluoropolymer film. The foil is patterned using etching resists that are patterned on the foil by photolithography or by screen printing according to techniques used in the flexible circuitry industry. The back contacts on the photovoltaic cells are adhered to and electrically connected to the foil circuits by adhesive conductive paste. Adhesively bonding metal foil to a carrier material, patterning the metal foil using etching resists that are patterned by photolithography or screen printing, and adhering the carrier material to one or more protective back-sheet layers can be expensive and time consuming.
PCT Publication No. WO2011/011091 discloses a back-contact solar module with a back-sheet with a patterned adhesive layer with a plurality of patterned conducting ribbons placed thereon to interconnect the solar cells of the module. Placing and connecting multiple conducting ribbons between solar cells is time consuming and difficult to do consistently.
There is a need for a more efficient process for producing a back-contact photovoltaic module with integrated conductive circuitry for a back contact photovoltaic cell and for producing back-contact solar cell modules.